In general, for example, as shown in FIG. 1, a bent axis type axial piston pump/motor has been heretofore constructed such that a shaft 2 is rotatingly borne through a main bearing device 3 to a housing 1, that a central support pintle 5 supported by a cylinder block 4 and tilted at a predetermined tilt angle .theta. with respect to the shaft 2 is tiltably connected to the shaft 2, and that pistons 7 slidingly inserted into cylinder holes 6, respectively, of the cylinder block 4 are tiltably connected to the shaft 2.
In such a bent axis type axial piston pump/motor as described above, since the pistons 7 are connected to the shaft 2 at a position where the pistons 7 are offset in the outer peripheral side of the axis of the shaft 2, and further the pistons 7 are tilted with respect to the axis of the shaft 2, the pistons 7 are thrusted against the shaft 2 by a force F.sub.1 in the direction shown by an arrow due to a hydraulic pressure within the cylinder holes 6. As a result, a thrust load and a radial load are acted on the shaft 2.
Therefore, the main bearing device 3 is constructed such that first and second bearings 8 and 9 of a conical roller type are disposed in a tandem arrangement, and that both the thrust load and the radial load can be received continuously by connecting inner races 8a, 9a of the first and the second bearings 8, 9 and outer races 8b, 9b of the first and the second bearings 8, 9 through an inner wheel seat 10 and an outer wheel seat 11, respectively.
In such a main bearing device 3 as described above, the thrust load Fa equally acting to the first and the second bearings 8, 9 as indicated by an arrow of perforated line in FIG. 2, but the radial load Fr.sub.1 acting on the first bearing 8 becomes greater than the radial load Fr.sub.2 acting on the second bearing 9, because the radial loads are acting tiltingly on positions, respectively, which are offset from the axis of each roller.
Therefore, the total load acting on the first bearing 8 becomes greater than that acting on the second bearing 9. As a result, the life of the first bearing becomes shorter, and hence the life of the main bearing device becomes shorter.